\[\frac{81^{- 3} \cdot 27^{- 5}}{9^{- 12}} = \frac{\left( 3^{4} \right)^{- 3} \cdot \left( 3^{3} \right)^{- 5}}{\left( 3^{2} \right)^{- 12}} =\]
\[= \frac{3^{- 12} \cdot 3^{- 15}}{3^{- 24}} = \frac{3^{- 27}}{3^{- 24}} = 3^{- 3} = \frac{1}{27}\]